<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* */
        .box1{
            background-color: red;
            height: 200px;
            width: 200px;
             /* 鼠标悬浮1秒后 以100秒直线运动 12-过度 */
             transition:1s 1s linear all;
        }
        /* 动态伪类选择器 */
        .box1:hover{
            height: 400px;
           
        }
    </style>
</head>
<body>
    <div class="box1"></div>
</body>
</html>